Production of liquid iron

ABSTRACT

The invention relates to a method for producing liquid in an electric melter or furnace. The method relates to producing liquid iron in an electric melter, utilizing highly reduced sponge iron, which is defined as sponge iron resulting from reduction of iron bearing material, and having a degree of metallization being in excess of 60%. (Metallization is expressed as analyzed metallic iron divided by analyzed total iron). 
     The method comprises transferring the highly reduced sponge iron, together with at least some residual carbon, to a melter in a hot state and substantially in the absence of oxygen. This avoids heat loss and reoxidation. The highly reduced sponge iron and residual carbon are then passed in a controlled manner, into the melter, where one or more electrodes operate in a low resistance mode.

CROSS REFERENCE TO RELATED APPLICATION(S)

This is a divisional application of Ser. No. 806,138, filed Dec. 10,1985, now U.S. Pat. No. 4,661,150, which is a continuation of Ser. No.721,499, filed Apr. 10, 1985, now abandoned, which in turn is acontinuation of Ser. No. 609,653, filed May 14, 1984, now abandoned, andwhich in turn is a continuation of Ser. No. 532,054, filed Sept. 14,1983, now abandoned.

BACKGROUND TO THE INVENTION

This invention relates to improvements in the production of liquid ironin an electric furnace of melter.

It is well accepted that there are a number of methods and arrangementsrelating to melting iron bearing materials, which utilise iron bearingmaterials in a partially reduced state. This then means that areasonably substantial amount of further reduction (and theconsequential use of further power) must take place in the furnace ormelter which is used for the production of liquid iron. As a result thisrequires high energy and power consumption which can be both a practicaland economic problem. In addition, when such partially reduced materialsare used in the production of liquid iron, further reduction of suchiron bearing materials has shown that the carbon content of theresultant liquid iron has been low and in some cases insufficient forfurther satisfactory processing.

Further, in methods and arrangements used up until this time, wherepartially reduced iron bearing materials have been used, there has beena problem with the type of iron bearing materials or ores that could beused. Thus, because of the difficulties inherent in using some ironbearing materials (particularly when in a partially reduced state), timeand effort has been required in the selection of the iron bearingmaterials, or feedstock. This is because certain materials (such as forexample titaniferous iron sand) have not been able to be effectivelyused in the production of liquid iron using methods and arrangementsused up until this time. In some methods used up until this time, theuse of such iron bearing materials has made it very difficult (if notimpossible) from a practical point of view, to accurately and adequatelycontrol the content and nature of the resultant liquid iron.

In addition, there has been a real problem in using fine iron bearingmaterial. Where partially reduced material is used in a furnace ormelter, substantial amounts of gases are formed during reduction withinthe furnace, and below the surface of the slag, formed on top of theliquid iron. The gas thus evolved, is the result of the only partiallyreduced nature of the iron bearing material and has up until this time,caused explosions and slag blows and boils within the furnace or melter.Where fine iron bearing material has been experimented with, it has beenfound inappropriate in such processes involving the use of partiallyreduced material. The fine iron bearing material or ore forming a slag,presents problems in that the gases below the surface will easily passup and rupture through the slag of the fine material, this again causingexplosions and slag blows and boils within the furnace or melter. Thishas detracted from the efficiency and general operation of methods andarrangements utilising partially reduced material, as used up until thistime.

By way of example only, in methods and arrangements used up until thistime, those skilled in the art would have generally been reluctant toutilise partially reduced iron bearing material which included by way ofexample only between 10% and 20% (by weight) below 6 mm in size. It willbe appreciated therefore, that methods and arrangements used up untilthis time have not been able to take advantage of a large amount of ironbearing material, due to the deficiencies and problems associated withthe methods and arrangements used and known up until this time.

As referred to hereinbefore, a further and very real problem associatedwith methods and arrangements used up until this time, is that whereonly partially reduced iron bearing material is used in a furnace ormelter, the energy consumption is high and a large amount of gas isformed. Thus, not only is this a problem from an economic and powersupply point of view, but the carbon content of the resultant liquidiron (resulting that is from the electric furnace) has in numerous casesbeen insufficient or at least unsatisfactory, for further processing oruse.

It is an object of this invention to provide a method and arrangementfor producing liquid iron in an electric furnace or melter whichovercomes or at least minimises the problems encountered up until thistime.

It is a further object of this invention to provide a method andarrangement for the production of liquid iron in an electric furnace ormelter which is straightforward and efficient in operation.

SUMMARY OF THE INVENTION

Throughout the specification and claims, reference is made to "highlyreduced sponge iron". The term is hereinafter defined throughout thespecification and claims as sponge iron resulting from reduction andhaving a degree of metallisation in excess of 60%. In this regard,metallisation is expressed as analysed metallic iron divided by analysedtotal iron. As referred to herein, methods and arrangements used upuntil this time have used partially reduced sponge iron which hasnormally been less than 50% metallised.

According to a further aspect of this invention there is provided amethod of producing liquid iron in an electric melter having one or moreelectrodes therein, comprising transferring sponge iron having a degreeof metallisation in excess of 60%, together with residual carbon, in ahot state, to said melter, substantially in the absence of oxygen;controlling the passage of said sponge iron and residual carbon intosaid melter operating said one or more electrodes within said melter ina low resistance mode.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described by way of example only, and withreference to the accompanying drawings, wherein;

FIG. 1: is a diagrammatic view of a process route according to one formof the invention.

FIG. 2: is a view of a melter as used in one form of the presentinvention.

FIG. 3: is a view of an example of a hot transfer vessel for use inaccordance with one form of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION

The present invention relates to the production of liquid iron in anelectric furnace or melter, hereinafter referred to throughout thespecification and claims, as a "melter"), using sponge iron which hasbeen highly reduced by reduction, such as in an appropriate reductionapparatus, arrangement, or kiln. As referred to hereinbefore, the term"highly reduced sponge iron", is herein defined throughout thespecification and claims, as sponge iron with a degree of metallisationin excess of 60%, with metallisation being expressed as analysedmetallic iron divided by analysed total iron. This definition of "highlyreduced sponge iron", is used throughout the specification and claims,to differentiate from other known processes that use partially reducedsponge iron, this being normally less than 50% metallised (typically 20%to 40%). Prior art literature and industrial practice disclose thatelectric melters have been fed with cold and hot partially reduced ironore, or other materials. The reduction of these materials has howevertypically been from 20% to 40% and thus the material has not previouslybeen highly reduced as is required and disclosed by the presentinvention. In addition, it is also well documented that highly reducedores can very easily reoxidise (with the consequent rapid rise intemperature that leads to scintering and agglomeration of the reducedmaterial).

It has been found in experimentation that it is preferable that thehighly reduced sponge iron of the present invention have a degree ofmetallisation being above 75%. It has been further found that ametallisation range of between 85% to 87% is particularly desirable. Itshould be appreciated however that this level of metallisation above 60%may change with different ore analysis.

The present invention therefore provides a method and arrangement forthe production of liquid iron using an electric melter, wherein anamount of highly reduced sponge iron is fed to the melter. The highlyreduced sponge iron is preferably transferred to the melter in a hotstate with residual carbon resulting from a previous reduction process(such as in a reduction apparatus or kiln). This then provides residualcarbon and superheat to assist in the hot transfer of the highly reducedsponge iron from the kiln to the melter. It also allows the liquid ironto be in a form having sufficient superheat and carbon, suitable forfurther steelmaking processes.

While reference is made to the highly reduced sponge iron beingtransferred in a hot state, and thereafter being passed into a melter,it should be appreciated that the transfer and passage into the melterneed not necessarily be at high temperatures. It should be furtherappreciated however, that if hot transfer and passage into the melterdoes not take place, a risk of re-oxidation increases; in addition,additional energy and power will be required in the melter.

The highly reduced sponge iron with residual carbon is transferred tothe melter in a hot state, preferably by means of one or moreappropriate transfer vessels, substantially in the absence of oxygen.Thus, the highly reduced sponge iron is transferred from the kiln to themelter without any major temperature loss and without any significantreoxidation.

One of the real problems with processes used up until this time, hasbeen the substantial energy requirements. In particular substantialelectrical energy requirements. Thus, by transferring the highly reducedsponge iron to the melter, in a hot state and substantially in theabsence of oxygen, there is a significant reduction in the requirementfor electrical energy by the melter for the melting of the sponge iron.In addition, and as referred to hereinbefore, a relatively high level ofcarbon is provided in the liquid iron, which is particularly suitablefor further steelmaking processes.

The present invention also allows for the use of highly reduced spongeiron in a fine form, (which has not been realistically possible up untilthis time). The highly reduced sponge iron is also able to be meltedeffectivley due to the relatively low volumes of gas generated in themelter, from the highly reduced sponge iron. Any gases evolved or formedin the melter (which are relatively small compared with the amount ofgases evolved in prior methods and arrangements), are able to escapethrough the fine material, forming at least part of a liquid slag withinthe melter, without (or at least substantially reducing) the danger ofexplosions or slag boils or blows. As will be appreciated, this is asubstantial advantage over previous and known methods and arrangements.In addition, the method and arrangement of the present invention allowsa substantially open pool or area of molten slag to form in a reactionzone or area (substantially about and adjacent to one or more electrodesin the melter). This also allows at least some of the gas formed, toescape through the pool, without the need to permeate through the slag.

In use, it is envisaged that the size of the fine ore or iron bearingmaterial will be such that generally about 60% (by weight) of thematerial will be between 106 microns and for example 212 microns. It isenvisaged that material used in large scale plants will allow for largerlumps of agglomeration of up to for example 150 mm.

Examples of the size of the iron ore, or iron bearing material used intrials are for example:

+300 microns: 15%

+212-300 microns: 7%

+150-212 microns: 23%

+106-150 microns: 42%

+75-106 microns: 13%

+53-75 micronss: 1%

-53 microns: Nil

The ability of the present invention to utilise presently used ores andfine ores (not previously considered suitable or appropriate), meansthat the present invention has a far greater application and an abilityto use a very great range of iron bearing materials.

The method and arrangement of the present invention also provides forhot, highly reduced, sponge iron to be fed or passed into the melter, ina controlled manner, through suitable control means, (such as valving,screw feeds or vibratory feeds), so that the amount of highly reducedsponge iron being fed into the melter is able to be closely controlledand monitored. In this manner, the power supplied to the one or moreelectrodes, for melting within the melter, can be accurately matched bythe energy required to meet the controlled feed of highly reduced spongeiron. This then also enables the slag and metal temperatures to becontrolled, this contributing substantially to the efficiency andoperation of the present invention.

The power fed to the one or more electrodes of the melter, preferablyhas its voltage and current controlled in an appropriate manner and byappropriate control means, such that the total energy supplied issufficient for melting within the melter, while the resistance issuitably controlled. This thereby permits a relatively high carboncontent liquid iron to be made with valuable vanadium in solution; whileno significant quantities of other metalloids (such as for examplesilicon, titanium or manganese) are present to any great extent.

In a preferred form of the invention, the highly reduced sponge irontogether with residual carbon, (preferably being substantially the totalkiln discharge with both residual carbon in the char and the highlyreduced sponge iron being mixed), is hot transferred (that is to saytransferred in a hot state substantially in the absence of oxygen) froma kiln or reduction housing or apparatus to the melter. It isadvantageous therefore, that the residual carbon in the char is present,in that this significantly assists in preventing reoxidation. This thenpermits the hot transfer to, and passage into, the melter, withoutsignificant heat loss or re-oxidation. It is to be appreciated thatthere is always a chance that some oxygen may be present or may enter atransfer container or vessel used for hot transfer; in such a case anyoxygen that may be present or may enter, is immediately combusted withsome of the residual carbon. This then will not effect the highlyreduced sponge iron or immediately effect the temperature thereof.Indeed, it has been found that during the hot transfer, any oxygenpresent will combust with residual carbon and a protective atmosphere ofcarbon monoxide will be generated and formed. This will then generallysubstantially prevent or minimise re-oxidation of the highly reducedsponge iron.

As will be appreciated, it is desirable that the highly reduced spongeiron be transferred in a hot state, such as from the kiln to the melter.It is also highly desirable that re-oxidation be prevented (or at leastminimised) during such hot transfer. As indicated hereinbefore, in thepreferred form of the invention, residual carbon is transferred to themelter together with the highly reduced sponge iron.

If however, only a small amount of carbon is present during the hottransfer, an artificial atmosphere (such as for example a reducing gasor nitrogen), can be introduced into the container or vessel used forthe hot transfer, this preventing or minimising contact between oxygenand the highly reduced sponge iron. Such a reducing gas or nitrogen willthen act as a substitute for (or in addition to), the carbon. It shouldbe appreciated that the provision of nitrogen is a highly desirablesafety feature, to prevent damage to plant when the kiln discharge isnot fully under control (such as for example during start up, shut down,or under emergency situations such as power failure).

Referring to FIG. 1 of the accompanying drawings, it will be seen thatfine iron ore and coal are used to form the highly reduced sponge iron.As referred to hereinbefore, the present invention allows for the use offine iron ores and fine iron bearing materials, such materials nothaving been capable of effective use up until this time. Preferably,coal is used in the reduction process, this avoiding use of expensiveelectrical power and thus saving on energy costs.

As will be appreciated from the foregoing description, the iron bearingmaterial (preferably in a relatively fine form), is highly reduced (suchas herein defined). The highly reduced sponge iron preferably togetherwith residual carbon, is then transferred in a hot state andsubstantially in the absence of oxygen to one or more melters.

The slag is removed from the iron melters and is tipped. Iron from themelters passes to a steel making vessel, whereafter it is formed intoslabs. In the preferred form of the invention as shown in FIG. 1 of theaccompanying drawings, the molten metal from the iron melter is passedinto a ladle, for the recovery of valuable elements such as vanadium.Slag from the steel making vessel is taken or passed to one or moreappropriate tips.

The highly reduced sponge iron (as herein defined), preferably togetherwith residual carbon, is transferred to a melter, preferably in a hotcondition and substantially in the absence of oxygen, in one or moreappropriate vessels or buckets. In alternative forms of the invention,the hot highly reduced sponge iron can be transferred by way of enclosedconveyors, or other suitable containers. In the preferred form of theinvention, it is however important that the highly reduced sponge ironbe transferred in a hot condition and without any substantial oxidationtaking place. Thus, in this way, the highly reduced sponge iron andresidual carbon entering or passing into the melter is still in a hotcondition having superheat properties, and still having valuable carbonproperties.

Referring to FIGS. 2 and 3 of the accompanying drawings, an appropriatevessel 1 used for the hot transfer is shown. The vessel 1 has a mainbody portion, with angled or slanted lowered sides 2, the vessel havingat least one inlet port 3 at an upper end thereof, and an outlet port 4at the lower end thereof. The inlet and outlet ports 3 and 4 areprovided with air-tight or sealable closures so as to prevent theingress of oxygen into the container 1, during the passage of the hot,highly reduced, sponge iron (into and from the vessel 1).

For example the vessel 1 is positively located under a hopper or bunker(not shown) at the end of, or connected to, a kiln, and into which thehighly reduced sponge iron and carbon are passed from the kiln, (andheld prior to hot transfer). A lower end of the kiln hopper is providedwith a suitable airtight or sealable valving arrangement, which engagesin an air tight seal, with the inlet port 3, so that the hot and highlyreduced sponge iron passes from the hopper into the transfer vessel 1,in a substantially oxygen free manner. The port 3 is then closed,avoiding as far as possible the ingress of any oxygen. The transfervessel 1 thereby holds the charge of hot highly reduced sponge iron andcarbon in a substantial oxygen free environment, and is transferred ortransported to a melter 10 in any appropriate method and by anyappropriate means. The vessel 1 is then placed over or adjacent themelter 10, so that the outlet 4 of the vessel 1 is capable of engagingwith an inlet 11 into the melter. Preferably, the melter 10 is providedwith a plurality of inlets 11 in an upper surface or roof thereof. Thiswill be described further hereinafter.

The lower or bottom end 1a of the vessel 1 is provided with a valve 15such as shown in FIG. 3 of the accompanying drawings, so that on theoutlet 4 of the vessel and the inlet 11 of the melter 10 beingjuxtaposed in a sealed position relative to each other, a sliding valve15 is moved laterally, allowing matter to pass from the transfer vessel1 into the melter inlet 11. The valving arrangement 15 includes forexample a plate 16 with a handle 17 at one end thereof, the plate 16being capable of being moved laterally of the transfer vessel 1 within agroove or space, between spring loaded seals 18, which abutt againstadjacent surfaces of the plate 16, thus forming a substantially airtight seal. To open the arrangement the handle 17 is gripped and theplate 16 is moved laterally outwardly, (such as in the direction ofarrow "A" in FIG. 3 of the drawings). This then opens the outlet 4 andallows it to communicate with the inlet 11 of the melter 10. Once it isdesired to close the opening from the vessel 1, the handle 17 is grippedand the plate pushed or slid inwardly, (so that it is in a positionsubstantially as shown in FIG. 3 of the drawings) and into a position inwhich the outlet 4 from the vessel 1 will be closed and sealed. Anoverflow chamber 4a is provided at the lower end of the vessel 1 andadjacent a material discharge outlet 4 so that excess material gatheredaround the outlet 4 (which material will be moved laterally or sidewayson the plate 16 being closed), will be able to overflow or exit throughthe overflow chamber 4a).

The above is however by way of example only. It should be appreciatedthat any appropriate and effective sealing arrangement and associatedcontrol or operating means can be provided in conjunction with the inletand/or outlet to the hot transfer vessel. A plurality of transfervessels can be used in conjunction with a plurality of inlets 11, intothe melter 10, if desired.

The vessel 1 is a refractory lined container, of any appropriate shapeand configuration, although one example of a shape and configuration isshown in FIG. 2 of the accompanying drawings, this allowing for straightforward and efficient transfer from the highly reduced sponge iron froma kiln to the melter.

If desired, one or more sealable inlets, 2a can be provided in thetransfer vessel 1, to allow for the ingress or entry of excess carbon,or one or more inert gases (such as a supply of nitrogen); especially toallow for the entry of nitrogen into the container should this bedesired (such as for the purpose of maintaining a relative high carboncontent and high temperature during transfer).

During experimentation, the handling of hot reduced primary concentratein various char mixtures ranging from 0 to 10% (by weight) has beenextensively tested, measured and observed. For example with batches ofup to 1300 kg in a pilot plant, at the completion of a reduction test,the reduced primary concentrate was tipped or removed by way of anenclosed chute and gate valve into the top of a refractory linedtransfer container or vessel. The temperature range varied from between800° C. and 1000° C. The refractory lined container had a lower conicalsection, and a sealed slide valve arrangement used to allow or permitthe hot material to discharge or pass into a melter inlet arrangement.This will be described further hereinafter.

As has been described hereinbefore, even a relatively small amount ofchar or residual carbon, present with the highly reduced sponge iron,will rapidly form a protective blanket of carbon monoxide, over thehighly reduced sponge iron, (this preventing or at least minimisingreoxidation). Reference has been made to an enclosed and substantiallyoxygen free container or vessel, but it should be appreciated that anopen topped container or vessel could be used. For example, an opentopped container or vessel, carrying highly reduced sponge iron(together with an amount of char or residual carbon from the kiln), islikely to have a protective blanket of carbon monoxide formed over thehighly reduced sponge iron (by the residual carbon reacting with theoxygen), this maintaining required heat and carbon content in the highlyreduced sponge iron.

For example, if a container is open topped, the carbon monoxide soformed will burn to carbon dioxide and the surface will rapidly cooldown to a temperature below which, significant further reoxidation willnot occur. Further, it should be appreciated that any reoxidation thatdoes occur would be restricted to a top layer of the material in thecontainer, which will thereafter crust over and prevent or at leastminimise further reoxidation of the material beneath the top layer orcrust.

In use however, and in the preferred form of the invention, when thecontainer or vessel is sealed in a substantially oxygen free manner,very minor (if any) reoxidation is likely to occur.

It should be appreciated that if any significant amount of air isadmitted into the container, reoxidation can be severe which can in turnlead to localised overheating and scintering together of the oxidisedmaterial.

It is therefore preferred that the container be substantially oxygenfree, and that the valving associated with the container or vessel besuch as to allow for a substantially air tight or oxygen freeenvironment within the container or vessel.

In one form of the invention, and utilising a container having acapacity of for example 10 tonnes of highly reduced sponge iron andresidual carbon, the following parameters were followed:

    ______________________________________                                        Temperature tested    600-1000° C.                                     Metallisation         78%-92%                                                 Char (Residual carbon)                                                                              0%-10%                                                  (By Weight):                                                                  Percent carbon        0-8%                                                    (By Weight):                                                                  ______________________________________                                    

In this case, measured loss of metallisation for the container or vesselwas between 0 and 2%, the holding time being for a period of up to 8hours.

The melter 10 of the present invention is an appropriate refractorylined housing having a base 26, side walls 27 and a roof or uppersurface 28; one or more (and preferably a plurality of spaced apart)electrodes 30 are located and housed within the melter 10, theelectrodes 30 being spaced apart from the underside 26a of the base, orbottom 26 of the melter 10.

Suitable outlets are provided in sides of the melter 10, adjacent thebase thereof; the outlets 32 and 33 allow for the tapping and release ofslag and liquid iron, from within the melter 10.

At an upper end or surface of the melter 10, preferably passing throughthe top or upper surface 28 thereof, one or more inlets 11 are providedso that highly reduced feed stock can be inserted or passed into themelter 10.

The inlets 11 are controlled inlets, provided with feed control means 35such as in the form of a vibratory feed, a screw feed or some otherappropriate means. Preferably, they are operable by an appropriate primemover or power means, and associated with adjacent or spaced apartappropriate control means to control the speed and operation of thecontrolled feed means 35. For example, manual controls or electrical,electronic or hydraulic controls can be used. The controlled feed means35 are provided within a feed housing member outwardly of the melter 10,the inlets 11 leading into and from the controlled feed means 35 intothe melter 10.

In the preferred form of the invention and as shown in FIG. 2 of theaccompanying drawings, the inlets 11 are adapted to be connected (as at11a), in a substantially oxygen free or airtight manner, to a lower endof a hot transfer vessel 1, to be controlled fed into the melter 10,such as described herein by way of example. In other forms of theinvention however, it is envisaged that other suitable transfer meanscan be used to control the feed of the highly reduced sponge iron from avessel 1, to the melter.

For example, in one form of the invention, a conveyor can be providedbeing a sealed conveyor or a tubular conveyor, which is provided with aninternal vibratory belt or screw feed, which is capable of beingcontrolled externally thereof, by suitable control means, so that theamount of highly reduced sponge iron being passed through the conveyorand into the melter is controlled. Also appropriate control valves andthe like can be used.

It is however, an advantage of the present invention that the passage ofhighly reduced sponge iron and carbon into the melter 10 is able to becontrolled and monitored by the feed control means 35, so that theamount of highly reduced sponge iron entering the melter 10 can becontrolled and monitored. Up until this time, no effective means havebeen provided for controlling the amount of such feedstock entering intomelters and this has created problems with control. In addition ofcourse, and as referred to hereinbefore such feedstock entering meltersup until this time has not been highly reduced, and thus a substantialamount of reduction has also taken place in the melter, in comparisonwith the present invention where the feedstock or highly reduced spongeiron has already been substantially reduced prior to entry into themelter. Thus, up until this time, there have been problems incontrolling and determining the standard (and in particular carboncontent) of liquid iron. The present invention overcomes, or minimisesthis problem.

Up until this time, the substantial amounts of feedstock or partiallyreduced sponge iron that have passed into melters have also createdproblems with control, having regard to the fact that a substantialamount of further reduction has been required in the melter; this hasresulted in the production of a substantial amount of gas which hascaused explosions and slag boils and blows within the melter. This hasalso resulted in excess power being required to maintain hightemperatures. Thus, there have been various problems in maintainingquality and control factors relating to carbon content within themelters.

In the present invention, where the feedstock is already highly reduced,and where passage into the melter is able to be controlled (togetherwith the operating resistance within the melter), these problems do notarise (or are minimal), so that there is a facility for a far greaterdegree of control and efficiency. Samples of the slag or liquid iron canbe taken at any time, and if it is desired to increase a carbon rate,excess or additional carbon can be entered through the inlets 11 in acontrolled manner. On the other hand, if it is desired to increaseoxygen levels within the melter, additional ore or oxygen can be enteredin a controlled manner also. Again, it will be appreciated that this hasnot been possible in previous melters, in that the combination of oreand a source of carbon has merely been entered or passed into themelter, following which reduction took place to a substantial extentwithin the melter, without the facility for control, that is provided bythe present invention.

It has been found in the present invention that by controlling the inputof the highly reduced feedstock, a burden 40 forms at the sides withinthe melter 10, above a lower liquid iron layer and an upper layer ofmolten slag.

In the present invention, the one or more electrodes 30 extend into themelter 10 and preferably extend below the surface 38 of the liquid slag.It has been found that in use this is more efficient in the product ofliquid iron, in that by having the ends 30a of the electrodes 30submerged in the liquid slag, radiation transfer from the electrodes 30to the inner surfaces of the melter 10 is substantially reduced, this inturn reducing or minimising refractory damage.

In addition, it has been found that by submerging the ends of theelectrodes 30 in the liquid slag, more effective turbulence is impartedto the slag during operation of the melter 10. In addition, it allowsfor a more effective heat transfer.

In the present invention, the operation of the melter 10 has been foundto be particularly effective by controlling both the input of the highlyreduced feedstock, and by a suitable selection of operating resistancetogether with electrical voltages, or currents, this thereby allowingthe carbon content of the resultant liquid iron to be accurately andeasily controlled to whatever level is desired. In particular towhatever level is desired for subsequent steel making processes.Furthermore, by controlling the same electrical parameters, the slag andliquid iron temperatures can be easily controlled to give temperaturesthat make both constituents suitable for further handling. Thistherefore allows the process to operate continuously and efficiently.

These same electrical parameters also permit control of the reductionwithin the slag of the melter of other oxides, such as for examplevanadium, silicon , titanium and manganese to provide the liquid ironwith required levels of dissolved oxides and solution that are suitablefor example for subsequent steel making operations.

Thus, it has been found most effective in the present invention tooperate the electrodes 30 in a low resistance mode, for the reasons setout above and to apply effective appropriate turbulence in theoperational or reaction zones about the one or more electrodes.

It should be appreciated that within the melter 10 various chemicalreactions are constantly occuring, these serving to give rise to asteady evolution of gas. At all times, there are various reductionreactions between residual iron oxide that has not been fully reduced tometallic iron in the previous direct reduction step, and carbon from thechar, that reacts to form carbon monoxide.

In a basic form, the reactions can be expressed by way of example as:

    Metal Oxide+Carbon→Metal+Carbon Monoxide.

Some of these reactions in detail can be expressed as:

    FeO+C→Fe+CO

    SiO2+2C→Si+2CO

    Ti02+2C→Ti+2CO

    V203+3C→2V+3CO

It should be appreciated that the reduced metal oxides dissolve intoliquid pig iron that has melted.

It has been found that by controlling the slag temperature and theamount of carbon that is contained in the char, (or fed with the highlyreduced sponge iron), the reduction of the metal oxides can beeffectively controlled to give selective reduction of vanadium and ironinto the liquid pig iron together with significant amounts of carbonwithout excessive amounts of silicon and titanium, by well known laws orthermodynamics commonly expressed as FREE ENERGY diagrams.

As referred to hereinbefore, the use of the highly reduced sponge iron(and in addition the minimal reduction of silicon and titanium), keepsthe amount of gas evolved in the melter to a minimum (especially incomparison with known methods and arrangements), this avoiding, or atleast minimising, the possibility of gas explosions or slag blows, withfine grain feedstock that is preferably used.

The gas that is evolved, tends to escape through small molten pools 50which form immediately and adjacent a reaction zone about the electrodes30 where the gas can therefore bubble through the molten slag and escapeto the surface atmosphere above the molten slag. In bubbling through themolten slag layer, escaping gas provides additional mixing and stirring,in addition to that imparted by the one or more electrodes 30 thisaiding in the homogenisation of the chemical composition and temperatureof the slag.

It is found therefore, that the controlled feed of the highly reducedsponge iron and the parameters referred to hereinbefore, result in areaction zones in the form of small molten pools 50 immediately adjacentor about the one or more electrodes 30, the reaction zone(s) havingturbulence imparted thereto by the electrode(s) and any escaping gases(as referred to above).

From pilot plant experimentation, the molten pool area from which gas isable to escape is formed or provided around one or more electrodes 30.For example three electrodes were provided and a pool was formed aroundand between the electrodes. Trials carried out with only two electrodesshow that gas tends to escape from the reaction zone immediatelyadjacent the electrodes and the area directly between each electrodewhich takes on a substantially dumbbell shape.

In one form of the invention it is envisaged that a plurality ofelectrodes may be provided; for example six electrodes in asubstantially rectangular melter. The electrodes can for example be sixelectrodes in line. It is anticipated that the gas will evolve aroundeach electrode and substantially along the centre line of the melterbetween the electrodes.

Experimentation carried out has demonstrated that there is a substantialrelationship between temperature and the reduction of metal oxides thatcan be effected by the carbon in the molten slag (as predicted bythermodynamics). Slag temperature should therefore be kept as low aspossible to minimise the reduction of silica and titanium, but not solow that viscosity becomes excessive and reduction of vanadium trioxidedoes not occur.

We have found that satisfactory operation can occur in the range forexample of 1450° C. to 1600° C. slag temperature, with a highertemperature being required in a pilot plant 1 tonne, or melter, comparedwith a 55 tonne furnace, due to higher heat losses. It is consideredthat a full scale operation should operate in the range of slagtemperature of 1420° C. to about 1550° C.

As referred to hereinbefore, it has been found in experimentation thatthe controlled feed of carbon with the highly reduced sponge iron is animportant control parameter, in order to maintain correct slagchemistry, that gives an appropriate low viscosity at low temperatures.Thus it has been found that entry of excessive carbon into the slag,will (as predicted from concentration effects in thermodynamics), givean excesslvely reducing situation. It is desirable therefore, tomaintain the slag with between 2 and 4% (by weight) FeO as this has beenfound to significantly reduce the viscosity and allow operation atrelatively low slag temperatures, while still maintaining good mixingand homogenisation of chemistry and temperature within the slag.

Referring to the slag, it has been found in experimentation in a pilotplant operation, that slag depths of up to 200 mm do not appear to haveany significant undesirable effects, provided viscosity is relativelylow and a good mixing is maintained.

In a 55 tonne furnace situation, slag depths of up to 500 mm have beenfound to work satisfactorily.

During experimentation, it has been found that trials with electrodes of130-300 mm diameter in a pilot plant and 460 mm diameter in a 55 tonnefurnace have shown no difference in operation of the process.

Various current densities have been experimented with, and it has beenfound that it is appropriate to use known electrodes such as for examplesoderberg electrodes, using about 5 amps per square centimeter ofelectrode cross section. In other forms of experimentation it has beenfound that current densities ranging from 6 amps per square centimeterto 35 amps per square centimeter of electrode cross section have workedsatisfactorily.

Hereinafter set out by way of example, is data and information relatingto the dimensions and parameters referred to hereinbefore in trials,carried out on 1 tonne and 55 tonne furnaces respectively.

    __________________________________________________________________________    MELTER OPERATION TRIALS                                                                           GOOD OPERATION                                                                             CONVENTIONAL OPERATION                                           1 t Furnace                                                                         55 t Furnace                                                                         1 t Furnace                                                                           55 t Furnace                         __________________________________________________________________________    FURNACE DIMENSIONS                                                            Shell Diameter (m)  1.5   5.0    1.5     5.0                                  Electrode Diameter (mm)                                                                           130    460   130      460                                 Electrode PCD (mm)  380   1340   460     1340                                 OPERATIONAL PARAMETERS                                                        Feed Wt/Tapping Wt  230-280                                                                             15000-20000                                                                          320-360 15000-20000                          (Metal + Slag) (kg)                                                           Power Input (at trans-                                                                            230-270                                                                             5800-6200                                                                            190-260 5000-6000                            former primary) (kw)                                                          Overall Operating   4.7-5.1                                                                             2.0-2.3                                                                              15-20   6-7                                  Resistance (m)                                                                Energy Consumption  190-230                                                                             8000-16000                                                                           280-360  8000-11000                          (KWh/tap)                                                                     FEED ANALYSIS (wt %)                                                          Fe.sub.m            58.3  57-56  58.0    56-59                                FeO                 11.8  14-13  9.0     10-15                                C                   4.7   4.8    4.8     4.5-5.5                              TAPPED METAL ANALYSIS (wt %)                                                  C                   3.5-4.1                                                                             3.2-3.6                                                                              1.7-2.2   2-2.2                              Mn                  0.17-0.27                                                                           0.15-0.25                                                                            0.34-0.42                                                                             0.14-0.24                            Si                  0.08-0.2                                                                            0.02-0.08                                                                            0.80-1.30                                                                             0.11-0.3                             Ti                  0.06-0.2                                                                            0.01-0.09                                                                            0.8 +   0.05-0.15                            V                    0.4-0.48                                                                           0.28-0.36                                                                            0.38-0.43                                                                             0.36-0.44                            TAPPED SLAG ANALYSIS (wt %)                                                   FeO                 2-3   3-6    0.5-1.5 0.5-2                                TAPPING TEMPERATURE (°C.)                                              Metal               1580-1600                                                                           1450-1510                                                                            1610-1670                                                                             1510-1580                            Slag                1450-1550                                                                           1480-1520                                                                            1600-1700                                                                             1570-1590                            ENERGY DISTRIBUTION                                                           Furnace Electrical Efficiency (%)                                                                 84     83    96       94                                  Furnace Thermal Efficiency (%)                                                                    75    80-90  75      80-90                                Furnace O/A Efficiency (%)                                                                        63    65-75  72      75-85                                Melting Requirement  950-1200                                                                            900-1050                                                                            1100-1500                                                                             950-100                              kWh/t Fein                                                                    __________________________________________________________________________

The invention has been described by way of example only and improvementsand modifications may be made without departing from the scope or spiritthereof, as defined by the appended claims.

We claim:
 1. A method of producing liquid iron in an electric melterhaving one or more electrodes therein, comprising transferring spongeiron having a degree of metallization in excess of 60%, together withresidual carbon, in hot state, to said melter, substantially in theabsence of oxygen; operating said one or more electrodes in said melterin a low resistance mode below about 5.1 mOhms, controlling (a)resistance of said one or more electrodes by resistance control means,and (b) passage of said sponge iron with the residual carbon into saidmelter by feed control means; so that carbon content of the resultantliquid iron and temperature in the melter are continuously monitored andcontrolled, while forming substantial liquid iron pools about andadjacent to said one or more electrodes in said melter.
 2. A method asclaimed in claim 1, wherein the passage of said sponge iron and residualcarbon into said melter, and the operation of said one or moreelectrodes in a low resistance mode, are carried out substantiallysimultaneously.
 3. A method as claimed in claim 1, using an iron bearingmaterial having about 60% by weight of said material between 0.06microns and 212 microns in size.
 4. A method as claimed in claim 1,wherein said sponge iron is transferred to said melter, substantially inthe absence of oxygen, in one or more substantially tight transfervessels.
 5. A method as claimed in claim 1, wherein said sponge iron istransferred to said melter substantially in the absence of oxygen and inone or more substantially airtight vessels, at a temperature of between800° C. and 1,000° C.
 6. A method of producing liquid iron in anelectric melter, using highly reduced sponge iron having a degree ofmetallisation in excess of 60%, and using an iron bearing material,wherein about 60% by weight of said material is between 106 microns and212 microns in size, comprising:transferring said sponge iron andresidual carbon to said melter substantially in the absence of oxygen;passing controlled amounts of said sponge iron and carbon into saidmelter; operating said one or more electrodes in said melter in a lowresistance mode; forming substantially liquid pools about and adjacentsaid one or more electrodes within said melter.
 7. The method of claim 1operating said electrodes in low resistance mode in the range of about2.0 mOhms to about 5.1 mOhms.